Method for anchoring a drilling rig in permafrost

ABSTRACT

A seismic rig first drills a shallow bore, about 10 feet deep, using its drill stem. The rig equipment is then used to set a retrievable anchor in the bore. The rig is moved and tied to the anchor. It is then in readiness to drill the main bore with increased penetration rate, since it is anchored.

United States-Patent 1191 Jackson 1451 July 23, 1974 METHOD FOR ANCHORING A DRILLING RIG IN PERMAFROST George Robert Jackson, R.R. 1, De Winton, Alberta, Canada Filed: Oct. 16, 1972 Appl. No.: 297,859

Inventor:

References Cited UNITED STATES PATENTS us. c1. 175/57 Int. Cl E211! 7/00,]

2,838,283 6/1958 Simmands et al 175/57 X 1 Primary Examiner-Geo. V. Larkin 1/192'4 Miller 175/230x Attorney, Agent, or Firm-Emest Peter Johnson 5 7] ABSTRACT A seismic rig first drills a shallow bore, about 10 feet deep, using its drill stem. The rig equipment is then used to set a retrievable anchor in the bore. The rig is moved and tied to theanchor. It is then in readiness to drill the main bore with increased penetration rate, since-it is anchored.

' 1 Claim, 6 Drawing Figures PATENTEU Jul 2 3 I974 SHEET 1 OF 1 METHOD FOR ANCHORING A DRILLING RIG IN PERMAFROST BACKGROUND OF THE INVENTION only a shallow bore (e.g., 50 to 100 feet in depth), the 1 weight of its drill'string is relatively small; hence the use of the pull-down means, which can increase the drilling weight by several multiples, is usually necessary in order to achieve desirable drilling rates.

In recent years, oil exploration has moved into the Arctic regions of North America. It is now common to fly seismic rigs into this area in large cargo planes. The rigs being used have been drastically reduced inweight in order to minimize the load transported by air. The

' weight of a typical seismic rig operation in the Arctic is about 10,000 pounds; Since only up to about onehalf of the rigs' weight can be brought to bear on the bit, even with the use of the pull-down means, the maximum unassisted drillingweight for a rig of this size is only about 5,000 pounds. s t

One way to increase the drilling weight under these circumstances would be to anchor the rig to the ground and use the pull-down mechanism to provide the needed additional force. However, in the Arctic the stratum adjoiningthe ground surface is usually comprised of permafrost. In simple terms, permafrost is ice containing solids such assand, clay and'the like. This material is too hard for one to dig a hole by hand in order to bury a log or other anchoring means totwhich the rig could be attached.

SUMMARY or THE INVENTION I bore to the work site would be greater than the amount which could be billed for drilling the bore. In this connection, we have found that the permafrost tends, with time, to freeze solidly around any motionless anchor which penetrates into it. For example, we have tried using an auger as an anchor; when the auger was to be removed, it would found to be solidly frozen into place and could not be retrieved.

It is therefore another object of the inventionto develop an anchor which is adapted to overcome the problem of permafrost freezing around it.

In accordance with the method of the invention, the rig is used to drill an anchor bore of relatively shallow depth. A retrievable anchor is set in the anchor bore,.

preferably using the rigs drill string to carry out the installation. The rig is then adjusted so that its drilling axis is adjacent to but spaced from the anchor bore. Usually this will be done by moving the entire rig a yard or twoover the anchor bore. The rig and anchor are fastened together and the relatively, deep main bore is then drilled, using a pull-down mechanism to provide a drilling weight, on the bit, which preferably is in ex? cess of the rig weight. When the main bore is complete, the anchor is retrievable, preparatory to moving on to the next drilling location. Preferably, the anchor is retrievable by moving the rig back over the anchor bore and using the drill string to collapse and remove the anchor.

Turning now to the anchor itself, it comprises two, basic components. The first component is a wing element which can be moved outwardly to the anchor bore wall to tightly abut or penetrate it. This component functions to lock the anchor to the bore wall. The second component is, adapted to displace the wing element into and out of engagement-with the anchor bore wall. The second component is designed to be inwardly spaced from the anchor bore wall; therefore it cannot be immobilized by the permafrost. If the wing element is frozen in place, the displacing component can break it free and collapse the tool.

, The gist of the invention lies in taking advantage of the mechanical power of the rig to provide a separate anchor-receiving bore; fixing an anchor in the bore and connecting it with the rig to enable the pull-down to operate; and utilzing an anchor which can be positively collapsed to free it from the permafrost. By the application of the invention, a seismic rig weighing 10,000 pounds can bring a drilling weight of. 1 5,000 pounds to bear on the bit, thereby greatly increasing the drilling speed capability of the rig.

- DESCRIPTION OF THE DRAWING In the'drawin'g: A FIG. I is a perspective view of the anchor; FIGS; 2 e 5 inclusive illustrate the operations involved more specifically;

FIG. 2 shows the anchor bore being drilled;

FIG. 3 shows the collapsed anchor positioned in the anchor bore;' 7

' FIG. 4 shows the anchor after is has been expanded; FIG. 5 showsthe anchor in place and the drill string of the rig drilling the main bore;

FIG. 6 is a perspective view of the rear of a seismic i se d t9 t e amber. ailies. t am a DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 1, the anchor 1 comprises a shaft 2 which is threaded at its lower end. Solid collar 4 3 and nut 4 are fixed to the shaft 2 at its end. A sleeve,

5 is mounted on the shaft 2 beneath the collar 3. The

shaft 2 is free to rotate within the sleeve 5. An internally-threaded travelling collar 7 is mounted on ,the threaded portion of the shaft 2. A pair of activating arms 8 are pivotally'connected at their lower ends to the travelling collar 7. A pair of upper arms 9 are pivotally connected at their upper ends to the sleeve 5 and at their lowerends to the upper ends of the activating arms 8. A stop collar 10 is threaded on the-lower end of shaft 2 to limit the downward movement of the travelling collar. i

In use, the anchor '1 is dropped into the anchor bore 11. The rig drill stem 12, equipped with a socket (not shown), is fitted over the nut 4 and rotated. As the shaft 2 turns clockwise, the travelling collar 7 moves upwardly; thereby causing the upper arms 9 to also move upwardly and outwardly into firm contact with the anchor bore wall. The drill stem 12 can be torqued up to firmly set the anchor in place. To collapse the anchor the drill stem 12 is again connected with the nut 4 and rotated counterclockwise to cause the travelling collar 7 to move downwardly and pull the arms9 out of contact with the anchor bore wall.

It is self-evident that various equivalents of the anchor 1 will occur to those skilled in the art. For example, one could use a hydraulic cylinder as the means for expanding the wing element. It is therefore to be understood that the scope of the invention isto be measured by the claims and is not to be restricted to the ment shown in the drawing.

The method of the invention can'be easily understood with reference to FIGS. 4 6. It involves drilling a shallow anchor bore 11 with the rig stem 12, setting the anchor l in the bore 11, connecting the rig 13 to the anchor 1 by means such as the cables 14, and then drilling the main bore 15 using pull-down means (not shown) to apply force to the drill string.

l. A method of drilling with a seismic rig having a drill stem and bit, which comprises:

drilling a relatively shallow anchor bore; setting a-retrievable anchor in the anchor bore; adjusting the rig so that its drilling axis is adjacent to I but spaced from the anchor bore; fastening the seismic rig to the anchor; and drilling a relatively deep vmain bore with the rig while maintaining, during at least part of the 'main bore drilling step, a drilling weight on the bit which is substantially in excess of the weight of the rig itself; and

retrieving the anchor.

embodi- 

1. A method of drilling with a seismic rig having a drill stem and bit, which comprises: drilling a relatively shallow anchor bore; setting a retrievable anchor in the anchor bore; adjusting the rig so that its drilling axis is adjacent to but spaced from the anchor bore; fastening the seismic rig to the anchor; and drilling a relatively deep main bore with the rig while maintaining, during at least part of the main bore drilling step, a drilling weight on the bit which is substantially in excess of the weight of the rig itself; and retrieving the anchor. FIG. 6 is a perspective view of the rear of a seismic rig, connected to the anchor, drilling the main bore. DESCRIPTION OF THE PREFERRED EMBODIMENT 